The Structure of Plant Cell Walls

Abstract

Degradative enzymes have been used to obtain defined fragments of the isolated cell walls of suspension-cultured sycamore cells. These fragments have been purified and structurally characterized. Fragments released from endopolygalacturonasepretreated cell walls by a purified endoglucanase and the fragments extracted from these walls by urea and alkali provide evidence for a covalent connection between the xyloglucan and pectic polysaccharides. Fragments released by a protease from endopolygalacturonase-endoglucanase-pretreated cell walls provide evidence for a covalent connection between the pectic polysaccharides and the structural protein of the cell wall.Based on these interconnections and the strong binding which occurs between the xyloglucan and cellulose, a tentative structure of the cell wall is proposed.The polymer composition and partial structures of the pectic and hemicellulosic components of isolated sycamore cell walls are described in the preceding papers (6, 26). There remains the problem of how these components are connected to make a functional wall matrix. It has been suggested that the wall is held together by noncovalent interactions between the various macromolecular components (20). However, the evidence presented in this and in the preceding papers suggests that, with the exception of cellulose, the macromolecules of the wall are covalently cross-linked, and that even the linkage between cellulose and the other cell wall polymers has the strength of a covalent bond.

A xyloglucan oligosaccharide‐active, transglycosylating‐D‐glucosidase from the cotyledons of nasturtium (Tropaeolum majus L) seedlings – purification, properties and characterization of a cDNA clone

“…Unlike the primary cell wall xyloglucans, seed xyloglucans are very easily extracted from the plant tissues with hot water (Reid, 1985). Their ease of extraction may be attributed to the absence in the apparently cellulose-free storage cell walls (Reis et al, 1987;Ruel et al, 1990) of the strong cellulose-xyloglucan hydrogen bonding (Keegstra et al, 1973) that is characteristic of primary cell walls. Seed xyloglucans are of very high molecular weight when extracted, and their solutions in water are of high viscosity.…”

Characterization and Expression of Four Proline-Rich Cell Wall Protein Genes in Arabidopsis Encoding Two Distinct Subsets of Multiple Domain Proteins

“…Interestingly, two soybean PRPs containing this motif were not substrates for this enzyme in vitro (Schnabelrauch et al, 1996). Pectin/extensin cross-links have been identified in cotton cell walls (Qi et al, 1995) and are thought to occur through either a 3,6-linked galactan or a ferulated sugar/amino acid cross-link (Keegstra et al, 1973;Brownleader and Dey, 1993). Thus, the insolubilization of the AtPRPs may involve either protein/protein or protein/carbohydrate linkages within the cell wall, and further investigation will be needed to determine if and how the cross-linking of these proteins within the wall contributes to the structure of the extracellular matrix.…”

Revision of adsorption models of xyloglucan on microcrystalline cellulose

“…The cellulose-xyloglucan network is embedded in a highly hydrated matrix composed of pectin and other hemicelluloses (Carpita and Gibaut 1993). The cellulose-xyloglucan network constitutes the major load-bearing structure of the primary cell wall (Keegstra et al 1973;Verbelen and Vissenberg 2007). It is also thought to act as a spacer preventing cellulose microfibrils from aggregating (Thompson 2005).…”